Tidying up white matter: Neuroplastic transformations in sensorimotor tracts following slackline skill acquisition.

This study investigated changes in white matter (WM) morphology following complex motor learning, that is, the learning to walk a slackline. A sample of young adults from the general population underwent brain imaging before the slackline intervention, after successful learning, and after a subsequent follow-up period by applying state-of-the-art measures for the assessment of micro- and macrostructural characteristics of WM fiber tracts (voxel-based and fixel-based). A randomly assigned control group (CG) was scanned at the same time points of assessment but received no intervention over the study period. Learning to walk a slackline resulted in manifold changes in WM morphology: (1) Whole brain fixel-based analyses revealed robust increases in the fiber cross-section in bundles closely associated with sensorimotor functions (e.g., superior longitudinal fasciculi, corticospinal tract); (2) The neurite orientation dispersion and density imaging (NODDI) parameters showed widespread decreases in overlapping fiber bundles. In the CG, no time-related WM changes were apparent at all. This well-controlled longitudinal intervention study provides substantial new evidence that learning a complex motor skill modulates fiber organization and fiber density in sensorimotor tracts.